This is the second high-profile cyber attack in a little more than a month on important computer networks that are increasingly seeming vulnerable to cyber attacks. A cyber attack on Sony’s PlayStation Network (PSN) led to hackers stealing sensitive information from potentially more than 100 million PSN and Station.com users. Hackers were able to break into Sony’s network on April 19, forcing the company to bring it down and beef up security.

Lockheed Martin said it thwarted the “significant and tenacious” attack on its information systems network that took place on May 21, according to a report by Reuters. The U.S. Department of Defense is working with the defense contractor, which builds major weapons systems ranging from fighter jets to ships for the U.S. government, to find out how the cyber incident affected the company and whether any information was compromised. The U.S. Department of Defense is also working with the company to offer recommendations that will help secure its network and prevent future intrusions, the company told Reuters today.

Lockheed Martin’s network contains sensitive data about contracts and defense technology that is currently in development. The network also holds sensitive information about state-of-the-art technology that is deployed in Iraq and Afghanistan — possibly similar to the stealth helicopter used in a raid that lead to the death of Osama bin Laden. The government did not say whether any sensitive information was compromised from Lockheed Martin’s private network.

The defense company recently made news after it purchased a state-of-the-art 128-bit quantum computer from quantum computer manufacturer D-Wave — one of the first commercially available quantum computers — which could be applied to security and advanced encryption projects. The purchase seems oddly appropriate given the highly sensitive information that might have been compromised in the company’s latest cyber incident.